A mobile device in mobile and non-mobile communication networks is commonly referred to as user equipment (UE). UE cooperation enabled by device-to-device (D2D) connectivity has been identified as an integral part of a fifth generation (5G) radio access virtualization framework.
Direct mobile communication between two UEs requires that the UEs and/or the network (NW) “discover”, i.e. detect the presence of neighboring devices which can be identified as potential helpers in virtualized radio access networks.
For 5G device-centric networks, UE discovery has many of the same functionalities as the cell search procedure in current 4G cell-centric networks. For instance, there is symbol and frequency synchronization in order to demodulate the control and data channels, there is acquisition of frame timing of the cell, and there is determining the physical-layer cell identity
Different levels of network involvement enable the UE discovery to be autonomous, network assisted, or network controlled. Virtualized radio access envisions an always-on connection state that relies on device-centric dedicated connection signatures (DCSs) that enable network-wide or region-based tracking of UEs. Due to mobility, network topology changes, therefore the UEs must update their neighbor's list periodically. Since many devices may simultaneously send their discovery signals, the discovery signals should not suffer from near-far effect, multiple discovery signals should be distinguishable, and energy consumption and UE battery drainage are important considerations as well.